Process of removing hydrogen embrittlement of bright nickel electrodeposits



Patented Dec. 19, 1950 PEOGESS F REMOVING HYDROGEN EM BRITTLEMENT 0F BRIGHT NICKEL ELEC-- TRODEPOSITS' Arthur S.

Kasper, Detroit, Mich assignor to Houdaille Her'shey Corporation, Hetroit, Mich, a corporation of Michigan No Drawing, Application April 3,. 1948-, Serial No. 18,853

Claims.

amount of hydrogen is evolved during the electrodeposition of chromium from chromium plating baths. As much as 35,000 volumes of hydrogen may be liberated at the cathode, or work, for

each volume of chromium deposited. A. portion of the hydrogen thus produced in'the chromium j plating operation is absorbed by the underlying nickel deposit and also by the base metal. In some instances, as will be pointed out, the absorption of hydrogen by the nickel deposit deleteriously affects the physical properties of the deposit.

Gray nickel deposits obtained by the use of Watts baths are ductile but require considerable buffing to obtain a mirror-bright coating suitable for subsequent chromium plating. The ductility of such buffed nickel deposits is not adversely affected by the occlusion ofhydrogen by the nickel deposit and by the base metal during chromium plating.

Bright nickel deposits obtained by the use of modified Watts baths containing organic sulfur compounds or similar organic additives are bright but non-ductile as initially deposited, so

that any embrittlement which may occur due to the occlusion of hydrogen during chromium plating produces no material change in the properties of the deposits. Bright nickel deposits produced as an alloy of cobalt and nickel are not believed to be embrittled' during chromium plating. A process, however,- which avoids the use of high percentages of cobalt will be mor economical.

For these reasons, the occurrence of hydrogen embrittlement and the provision of methods for alleviating the harmful effects of such embrit-i tlement have not assumed any great importance in the chromium plating industry. It has, however been proposed in the literature that hydrogen embrittlement be removed by heating achromium plated object to a temperature siifil-' ciently high to drive theoccl-uded or absorbed hy'-- The copending application of W. E. Jenks,

Fitzsimmons and Frank Ammermanu, entitled Method of and Bath Composition for Bright Nickel Plating, United States Serial No.- 775,748, filed September 23-, 1947, and'assigned to: the assignee of the present invention, discloses a bright nickel plating bath comprisingan aque-. ous' acid solution of nickel salts containing: aminor' amount of saccharin and co'umarinu The nickel deposits obtained by the practice:- cf the Jenks et al. disclosure are ductile andmirror-bright,- requiring littleor no polishing; Panels coated with such ductilebright nickel deei. posits may be bent-or'otherwise deiormedlbeyond; the elastic limit of the base metal without crack-z; ing or otherwise damaging'the deposit. huch a combination of brightness and/ductility has not been attained by the practice of the nickel plat-; ingprocesses of the prior art. 1 5.1:

The ductile, mirror-bright nickel depositsvof. Jenks et a1. are'very desirable for use: as: agLlIP-f termediate coating in chromium plating opera .w tio'ns'. However, it has been found that the due;v tile, bright nickel deposits of .Jenks et al. readilyabsorb hydrogendu-ring the chromium plating operationand that the occlusion of the hydro -i gen by the nickel deposit results in hydrogen .emr; brittlement of the. nickel layer. I have found; that the ductility of the nickel deposit cannot berestored by heating" the deposit to the tempera tures disclosed in the prior art. I e chromium layer, even when deposited upon the nickel plated; surface as a very thin; decorative coating, acts; as.- a barrier to prevent the escape of the occluded; hydrogenfrom the base metal and the nickel deposit. In order to impartsuificient energy to the entrapped hydrogen sothat it mayv escapethrough the chromium barrier, it is necessary to heat the chromium plated object to temperatures ranging. from 350 F. upwards. v I have found that such heating adversely affects the ductility. of the nickel deposit of J enks et al. even though;: the occluded hydrogen is driven off. Temperalj tures low enough to avoidthe thermal tlement of the nickel deposit are not sufficient to drive the hydrogen through the chromium layer to effectively restore the ductility of the nickel deposit.

The present invention now provides a process for removing hydrogen embrittlement from nickel deposits without causing further embrittlement of the deposit by excessive heating. I have discovered that ductile nickel deposits, such as those deposited upon a base metal as taught by the copending Jenks et al. application, may be heated to temperatures of about 300-324 F. for a short period of time, or at lower temperatures for relatively long periods of time, without materially impairing the ductility of the deposit. I have also found that such temperatures are effective to remove absorbed hydrogen from the nickel layer and from the base metal in the absence of an all-enveloping chromium layer. Hydrogen embrittlement may be removed from a chromium plated object at relatively low temperatures by providin a nonchromium plated surface area on the object through which the absorbed hydrogen may pass. The absorbed hydrogen is relatively free to travel within the nickel deposit and the base metal and may be completely eliminated through any nonchromium plated area.

The process of the present invention therefore contemplates removing the hydrogen embrittlement of nickel deposits by subjectin the base metal and the nickel layer containing absorbed hydrogen to a temperature less than that temperature at which the nickel deposit becomes brittle. In the application of the process of the present invention to the removal of hydrogen embrittlement from deposits of nickel having a superimposed layer of chromium applied thereto, it is preferred that at least a portion of one surface of the chromium plated object be free of chromium so that the absorbed hydrogen may be eliminated from the article through that surface. This chromium-free surface of the object may be provided by either preventing the deposition of chromium on that surface or by removing the chromium from the surface after the entire article has been chromium plated.

It is, therefore, an important object of the present invention to provide a process for the removal of hydrogen embrittlement from bright nickel electrodeposits by subjecting the nickel deposits to a temperature surfliciently high to relieve hydrogen embrittlement but less than that temperature at which the nickel deposit becomes thermally embrittled.

It is another important object of the present invention to provide a method for removing hydrogen embrittlement of bright nickel deposits having a subsequently applied electrodeposit of chromium formed upon the nickel surface by providing a chromium-free portion of the nickel deposit through which the hydrogen may escape at temperatures less than those temperatures at which thermal embrittlement of the nickel layer occurs.

It is a further important object of the present invention to provide a process for removing hydrogen embrittlement from nickel deposits having a deposit of chromium applied thereon which comprises providing a surface free of chromium and heating the deposit to a temperature of about 300 F. or less to drive absorbed hydrogen through the non-chromium plated surface.

It is a still further object of the present invention to provide a process for the production of chromium plated objects having an intermediate layer of nickel free of hydrogen embrittlement which comprises depositing chromium from an electroplating bath upon said objects, subsequently removing the chromium deposit from at least a portion of the surface area of the object, and heating the plated object to a temperature of about 300 F. or less to drive absorbed hydrogen from the plated object and the nickel deposit.

It is a yet further important object of the present invention to provide a process for the chromium plating of nickel plated objects and the removal of hydrogen embrittlement of the nickel deposit which comprises the electrodeposition of chromium from a chromium plating bath upon said object while leaving a portion of the surface area of said object free of chromium and subsequently heating the plated object to a temperature of about 300 F. or less to remove absorbed hydrogen from the plated area and from the nickel deposit through the non-chromium plated surface area.

Other and further important objects of the present invention will be apparent from the disclosure in the specification and the appended claims.

The method of the present invention is particularly applicable to the removal of hydrogen embrittlement from ductile nickel deposits prepared by the process as taught by the above identified Jenks et al. application Serial No. 775,748. The broader ranges of proportions and ingredients and conditions of operation of the bath and method of Jenks et al. may be briefly summarized as follows:

Total nickel content 0.5 N -saturation Nickel chloride (NiC12.6H2O) 0.1-1.5 N Nickel sulphate (NiS'Oa'lHzO) 0.4 N-saturation Boric acid (H3303) 0-saturation Citric acid 0-saturation Saccharin (water soluble) 0.05-4.13 grams/liter Coumarin (C9He02) 0.01-1.3 grams/liter. Temperature 60 F.-boiling pH 1.8-'-5.'75 Current density (at plating surface) 16 144 amperes/ft.

The nickel deposits obtained by the practice of the Jenks et al. disclosure are bright, ductile relatively free from internal tensile stress and possess excellent scratch hiding properties. It has been found that a steel plate having nickel deposited thereon by the method of Jenks et a1. may be bent through an angle of without crackingor otherwise damaging the nickel deposits. The occulsion of hydrogen during the chromium plating process results in a substantial reduction in the ductility of the bright nickel deposit obtained by the use of the Jenks et al. or any equivalent plating method. For example, the originally ductile plate following chromium plating initially exhibits cracking in the form of minute cracks upon bending at an angle of approximately 8 to 10, but these minute cracks do not open further even when bent as far as 180. By the process herein described, it is possible to restore the ductility of the J enks et al. plate and to obtain a ductile coating of nickel and chromium. I have found that if the article is chromium arseore theabsorbedhydrogen-is driven off, the nickel.

deposits arenot suitable for use when. placed: under stress due to thermal embrittlement. By. the method ofthe present invention it pOSZ-- sible to drive on the absorbed hydrogen at. tern peratu-resmuchless than those. of the prior art. to avoidoverheating. the; nickel deposit to. cause. thermal embrittlement'.

In accordance with the preferred process of the present invention, one surface or at least a ortion of one surface of the nickel plated objectv is made chromium-free, either by not coating that surfacewith chromhun during the chromium. plating operation or by stripping: a. portion of the chromium layer from, the nickeldeposit or base metal. The deposition of chromium upon a nickel plated surface may be prevented during the chromium plating operationby means of a tight- 1y; fitting mask of suitable insulating material. alternatively a conductor in the formof a sec.- ondary cathode or robber may be. employed toprevent. deposition of chromium upon a portion the nickel. plated surface. Any other suitable method of. preventing deposition. of. chromium maybe. employed. If desired the nickel plated article may be completely plated with chromium and the'chromium removedfrom a portion of the surface. by stripping, i. e.. by the use of hydro- Qhloric acid or other stripping agent, or by abrasion. Theinonechromium plated area inthe finished article may be sprayed with aluminum or other corrosion. resistant material so that the exposednon-chromium lated area may be protectad from corrosion.

Eollowing v the preparation of the chromium platedobject with one surface or a portion, ofv a surfaceiree of chromium, the occluded hydrogen present in. the nickel layer and in the. base ma,- terial may. escape from the non-chromiumplated surface. I have found that,v while hydrogen em- :bri-ttlementmay be relieved by aging the plated article at. room, temperatures, an aging period of from 4 to 10 days is necessary to restore.s .1ifi.- cient ductility to. the nickel deposit- If more rapid removal of occluded hydrogen is. desired, thernickekdepositlmay be heated to. temperatures. of about 300 or less to restore ductility to the deposit without causing appreciable thermal, embrittlement. The time necessary for the restorationv of ductility is an inverse. function of the temperature, and in order tov restore ductility Within a reasonable time, I prefer to. heat the deposit at temperatures of from 156. to 369 F. for. periods of. time ranging from several hours to I5 minutes.

The. following examples will serve to illustrate the method of the present invention and the conditions. under which the ductility of the nickel. deposit may b restored.

EXAMPLE 1' Steel test-panels were cleaned by a suitable procedure for use. as test panels in this and the other examples given herein. An aqueous solution containing both nickel chloride "and nickel sulfate was. prepared. The total concentration ofnickelin a bath was 2.9% N, the bath containing 0.4 N nickel chloride and 2.5 N- nickel sulfate.- The bath was prepared as follows: the desiredamounts of NiCIaGIIitQ and NiSQ aYH-EQ were dissolved in water togive. a 2.9 N nickel solution. The solution was maintained at a temperature of 125 F. 0.4 gram of coumarin per liter of solu- 5; tion was added to the solution by suspending the coumarin in a small amount, approximately 250 ml.,, of the nickel solution at atemperature of about 150 li.., or above, and pouring the suspension into the larger body of solution. 0.25 gram of soluble saccharin per liter of" solution was added by dissolving the proper amount in a,

small amount of waterand adding theresulting, Su-flicient boric' acid to give a 0.6 N solution (about 37.5- grams solution to the nickel solution.

1-5 per liter) and sufficientcitriclacid to give a concentration of 1.0 gram per liter was added to the plating; solution- ThepI-Lof the. platinasolution was maintained. ate value of 3.9-. The plates were plated inasolution at. a current density of.

20. ea amperes. per square foot at the race of the panel. Followinsthearemoval oi the nickel plat d steel plates. from-the. bath. the. plates were heated;-

atv the-indicatedtemperature for the time-listed in Fable-I. To. determine the. ductility of the niekellplated steelplates. a simple bend testw-as employed- This. test involves clamping the plate. in a. vise and bendingitby strikingit with. a ham mer. The piece was bent. until cracking wasob served and the amount of bending. was deter 30 mined. The resultslisted in Table I were obtained:

Table- I Amount'oi Treatment Temperature 532338 5: Bend Before Cracking Mi mttey Degrees Room temp. none 9o EXAMPEEI'Z To determine the efiect of. aging time at room temperatures, steel. plates, nickel lated in accordance with the disclosure of Jenks et al., as described in Example 1, were chromium plated in a. conventional chromic acid-sulfate bath. Following the: chromium plating operation, the lay Table II Amount'of. Bend Before A ing 'lime at. Room. Temperature Cracking" Degrees EXAMPLE 3.

chromium layer on both sides was: retainedon certain reference panels.

7 The following results were obtained:

Table III Amount of Bend Before Cracking Duration of Treatment Treatment l empemtufe C hromium Chromium Plated Plated Both Sides One Side Degrees Degrees Room Temp -8 none 45 min 3 hrs EXAMPLE 4 In order to determine more definitely the relief of hydrogen embrittlement by the process of the present invention, the ductility of nickel and chromium plated plates were tested by means of the Orlickson cup test. This test involves pressing a steel ball against a specimen so that the amount of deformation of the specimen may be measured up to the point that cracking of the deposit occurs. This test provides a means for definitely measuring and describing the ductility of a metallic coating. The following results were obtained by subjecting four specimens to the Orlickson cup test:

Specimen No.1 was nickel plated as described in Example 1.

Specimen No. 2 was nickel and chromium plated as described in Example 2.

Specimen No. 3 was nickel and chromium plated as described in Example 2, the chromium layer was stripped from one surface, and the specimen was tested immediately after stripping.

Specimen No. 4 was prepared as specimen No. 3 and tested after heat relief at 300 F. for min utes.

Table IV Specimen N o. Deformation face of the plated object so that hydrogen embrittlement is greatly reduced. It is preferred that the plated object be heated to temperatures ranging from 150 F. to 300 F. in order to efiect rapid removal of the hydrogen, although hydrogen embrittlement may be efiectively removed by aging for relatively longer periods of time at room temperatures.

It will, of course, be understood that various details of the process may be varied through a;

wide range without departing from the principles of this invention and it is, therefore, not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claims.

I claim as my invention:

1. A process for relieving hydrogen embrittle-- ment of ductile bright nickel deposits formed as an intermediate layer on a metallic object andhaving a superimposed layer of chromium elec-v trodeposited thereon, which comprises providing. a chromium-free surface area on the plated object and subsequently heating the object to a temperature of from 150 to 300 F. for a period of time ranging from about 15 minutes to several hours, the specific period being correlated with the treating temperature with a shorter heating period being employed with higher temperatures 2. The method of producing a ferrous foundation metal article having a relatively ductilenickel plate and a chromium plate thereover,

which comprises electrodepositing a ductile, bright nickel plate on a ferrous foundation metal,

electrodepositing chromium over a portion of said nickel electrodeposit and leaving another portion of said nickel surface exposed, and heating said article at a temperature of about 300 trodeposit for a period of time ranging fromf about 15 minutes to several hours.

3. The method of producing a ferrous foundation metal article having a relatively ductile nickel plate and a chromium plate thereof, which comprises electrodepositing a ductile,

' bright nickel on a ferrous foundation metal from a bath containing nickel salts, coumarin and saccharin, electrodepositing chromium over saidnickel electrodeposit, removing a portion of the chromium deposit to expose a portion of said nickel deposit and heating said article at a tem-' perature of about 300 F. to expel hydrogen through said exposed portion of the nickel: do

posit to relieve hydrogen embrittlement arising from said chromium electrodepositing step' with--';

out thermally embrittling said nickel electrodeposit for a period of time ranging from about 15 minutes to several hours.

4. In the method of producing a ferrous foun dation metal article having a ductile nickel plate and a chromium plate thereon by the electro deposition of a ductile, bright nickel deposit from a bath containing nickel salts, coumarin and saccharin and the electrodeposition of chromium on said nickel deposit, the steps which comprise stripping a portion of the chromium deposit from the plated article to expose a portion of said nickel surface and heating said article at a tem-j perature of about 300 F. to expel hydrogen through said exposed nickel surface whereby hydrogen embrittlement arising from said chromium electrodepositing step is relieved without thermally embrittling said nickel electrodeposit for a period of time ranging from about 15 min-' utes to several hours.

5. In a method of producing a ferrous foundation metal article having a relatively ductile nickel plate and a chromium plate thereover by" the electrodeposition of a ductile, bright nickel,

chromium on a portion of said nickel surface to expose a portion of the nickel deposit and heating said plated article at a temperature of about 300 F. to expel hydrogen through the exposed portion of the nickel deposit whereby hydrogen embrittlement of the nickel deposit arising from said chromium electrodepositing step is relieved without thermally embrittling said nickel electrodeposit for a period of time ranging from about 15 minutes to several hours.

ARTHUR S. KASPER.

REFERENCES CITED The following references are of record in the file of this patent:

Ser. No. 351,241, Weiner (A. P. 0), published May 18, 1943. 

1. A PROCESS FOR RELIEVING HYDROGEN EMBRITTLEMENT OF DUCTILE BRIGHT NICKEL DEPOSITS FORMED AS AN INTERMEDIATE LAYER ON A METALLIC OBJECT AND HAVING A SUPERIMPOSED LAYER OF CHROMIUM ELECTRODEPOSITED THEREON, WHICH COMPRISES PROVIDING A CHROMIUM-FREE SURFACE AREA ON THE PLATED OBJECT AND SUBSEQUENTLY HEATING THE OBJECT TO A TEMPERATURE OF FROM 150 TO 300*F. FOR A PERIOD OF TIME RANGING FROM ABOUT 15 MINUTES TO SEVERAL HOURS, THE SPECIFIC PERIOD BEING CORRELATED WITH THE TREATING TEMPERATURE WITH A SHORTER HEATING PERIOD BEING EMPLOYED WITH HIGHER TEMPERATURES. 